This invention relates to an oxygen absorbent composition which can absorb water, oxygen, acidic substances, etc., and optionally, which can also adjust humidity. This invention relates to an oxygen absorbent parcel formed by enclosing the above oxygen absorbent composition in a gas-permeable packing material which is impermeable to fine dust or capable of protecting the an article preserved from fine dust.
Further, this invention provides a method for use of the above oxygen absorbent parcel to suitably preserve metals, metal products, electronic products, electronic parts and components, dried foods, medicaments, photographs, ancient documents, pictures, pressed flowers, etc.
Japanese Patent Publication No. 040880/1987 proposes a method using oxygen absorbents containing catechol, ascorbic acid and a metal powder as essential ingredients. However, this method has a defect in that since these oxygen absorbents require a water content to absorb oxygen, a metal, when preserved, causes rust on its surface or an article preserved absorbs humidity due to transpiration of co-present water. In order to prevent this transpiration of a water content, Japanese Patent Publication Kokai No. 15378/1981 proposes a method using an oxygen absorbent and a desiccant in combination. In this method, however, a water content is transferred from the oxygen absorbent to the desiccant, and the oxygen absorption is terminated before required or the drying function is deteriorated.
As a method to overcome the above defects of the oxygen absorbent, Japanese Patent Publications Kokai Nos. 55641/1981, 198962/1988, 67252/1989 and 285973/1986 propose oxygen absorbents which require no water content to absorb oxygen, i.e. oxygen absorbents containing an unsaturated fatty acid compound as a main ingredient Since, however, the oxygen absorption rate and capability of these oxygen absorbents are low, it is required to increase the amount of an oxygen absorbent composition in order to achieve sufficient oxygen absorption, and when an article is preserved in a container for a long period of time, the oxygen concentration in the container sometimes gradually increases due to the article preserved and oxygen and water which have penetrated the container to some extent. Therefore, the expected effect on preservation has limits.
It is the first object of this invention to increase the oxygen absorption rate and oxygen absorption capability (maximum oxygen absorption) of the above oxygen absorbent composition and provide fields of article preservation technologies with an oxygen absorbent composition which can secure preservation of an article as long as possible in as small an amount as possible.
In preservation of paintings, calligraphic works, antiques and photographs, it is conventional Practice to enclose these articles and a desiccant together in a container and seal the container, since humidity is considered to have a bad influence. When these articles are preserved for a long period of time, however, a satisfactory effect is not always obtained, and undesirable phenomena such as color fading and "cracking" are found.
In order to overcome the above defects, Japanese Patent Publication Kokai No. 198962/1988 discloses a method for adjusting the oxygen concentration inside a sealed system to not more than 0.1% by means of a small gas-permeable parcel containing an oxygen absorbent which requires no water content for oxygen absorption and a desiccant.
The above method is preferably usable to preserve metal products and semiconductor devices since the humidity inside the sealed system can be decreased considerably. However, it is difficult to apply this method to the preservation of articles which undergo a chemical change or biological deterioration due to the presence of oxygen and which undergo physical fracture due to an influence of water (e.g. cracking and peeling when the articles are dried excessively or swelling and fusion when too much an amount of water is present).
Examples of such articles are ancient documents, ancient books, photographs, specimens, medicaments, magnetic tapes, etc. No good methods have been available, or it has been difficult, to preserve these articles well.
It is the second object of this invention to provide an oxygen absorbent composition which can easily maintain any degree of humidity optimum for preserving an article and which absorbs oxygen or an acidic substance inside a system.
For rust prevention of metals, metal Products, electronic products, electronic Parts and components, etc., during the preservation thereof, it has been attempted to enclose a composition having rust-preventing activity such as silica gel, volatile rust preventive, or the like in a gas-permeable packing material, enclose the resultant Parcel and an article together in a container and seal the container.
However, fine powders adhere to a surface of this rust preventive parcel when the parcel is produced or when the composition is enclosed in a packing material, and the fine powders contaminate an article preserved or cause a short electrical circuit.
When a rust preventive is exposed to atmosphere for a long period of time before enclosing it in a container together with an article and sealing the container, various defects arise. For example, the performance of the rust preventive is degraded, or it is impossible to sufficiently prevent water or an acidic substance from forming rust.
It is the third object of this invention to develop a rust preventive parcel which has a surface devoid of fine powders, which exhibits performance undegradable even if exposed to atmosphere before use, and which sufficiently prevents water and an acidic substance from forming rust, and to use such a rust preventive parcel to preserve electronic parts, electronic products, semiconductor parts and semiconductors.
When a parcel packed with a rust-preventive composition is used to preserve electronic parts and products, parts for semiconductor devices in particular, and materials for manufacturing semiconductor devices, a packing material formed of a laminate of paper and a porous plastic film is used as a gas-permeable packing material. However, when this packing material is used to pack a rust-preventive composition, dust floating in air adheres to a surface of the packing material under the attraction of static electricity of the packing material. It is undesirable to use such a rust preventive parcel as it is in order to preserve electronic parts and products, parts for semiconductor devices in particular, and materials for manufacturing semiconductor devices, since these articles preserved are contaminated, an electrical short circuit is formed, or rust is formed in circuits.
Meanwhile, Japanese Patent Publication Kokai No. 55075/1988 proposes a double-packed oxygen absorbent parcel formed by packing an oxygen absorbent parcel with a gas-permeable bag of a plastic film having pores measuring 0.2 to 2 mm in diameter. Since, however, diameters of the pores are large, dust of the oxygen absorbent composition passes through the pores, and the contamination with the dust cannot be prevented.
It is the fourth object of this invention to provide a parcel of which the packing material has a surface free from adherence of dust and prevents dust of a composition from passing through.
A photograph is widely and generally used to convey an image as information. However, substances constituting a photograph change with time, and it has been difficult to preserve a fixed image in an as-fixed state for a long period of time.
When a photograph is preserved under atmosphere having a high humidity, mold occurs in a gelatin layer used as a material, a base film contracts due to oxidation of a dyestuff or a change in humidity, or a dyestuff alters in properties due to a reducing substance present in air.
There is a method for preserving a photograph not by stabilizing photograph-constituting materials but by controlling an environment.
Japanese Patent Publication Kokai Nos. 88256/1986 and 167836/1989 disclose a method for preserving photosensitive materials with an antioxidant (specifically, an inert gas and/or an oxygen absorbent) and/or a desiccant. This method may be taken into consideration as it is in order to preserve a photograph for a long period of time. However, the defects of this method are as follows:
(1) When an inert gas is used as an antioxidant, it is impossible to reduce an oxygen concentration inside the system Preserving a photograph to a degree in which photograph-constituting substances do not undergo oxidation. Further, this method cannot be utilized easily since an apparatus for substituting an inert gas is required.
(2) A sealing method keeping an oxygen absorbent inside the system has an effect that an oxygen concentration can be decreased until photograph-constituting substances are not oxidized. However, water contained in an oxygen absorbent is sometimes transferred to a film inside the system to cause physical destruction such as fusion between the film and a packing material Further, in an iron-containing oxygen absorbent generally used, the absorbent absorbs oxygen and hydrogen is generated although its amount is small. Due to this dyestuff are altered in properties and preservation of a photograph is affected.
(3) In a sealing method keeping a desiccant inside the system, an alteration of a photograph is slowed since the humidity inside the system is decreased. However, a desiccant is not capable of inhibiting oxidation of photograph-constituting substances. Therefore, this method only has an effect of inhibiting occurrence of mold from the viewpoint of long term preservation, and cannot be applied in order to secure an image. Further, when the humidity inside the system is decreased excessively with a strong desiccant, physical destruction of photograph-constituting substances such as a crack and peel may arise. It is therefore required to determine a suitable amount of the desiccant, and such determination is difficult.
(4) In a method using an oxygen absorbent and desiccant in combination, water is essential for an oxygen absorption reaction, and the water is transferred to the desiccant to terminate the oxygen absorption reaction during a short period of time. In some cases, oxygen remains in the system. It is therefore very risky to employ such a method for long-term preservation.
It is the fifth object of this invention to preserve a photograph as it is for a long period of time by a simple method in which the photograph is enclosed in a container together with an oxygen absorbent and a desiccant.
A bearing for a rotor (to be simply referred to as "bearing" hereinafter) is mainly manufactured from a bearing steel, and packed and stored after rust-preventive oil is applied on it. Thereafter, a manufacturer of precision machines and electronic machines and components carries out steps of removal of the rust-preventive oil, application of machine oil, assembly, etc.
When a manufacturer manufactures a bearing as a part and delivers it to another manufacturer, the bearing is coated with rust-preventive oil or immersed in rust-preventive oil in order to prevent rust formation during the delivery from one manufacture to another and storage at a warehouse. Since, however, the rust-preventive oil is unnecessary or a hindrance at the assembly time, a washing step for removal thereof is required.
It is troublesome to carry out steps of applying a coating which is unnecessary or a hindrance for a future operation and removing the coating at a later time. It is naturally desirable to do away with such steps.
Further, the above washing step uses an organo-halogen-containing solvent such as Freon, trihaloethane, trihalomethane, or the like, and these solvents destroy an environment. It is therefore desired to reduce the use amount thereof
A bearing which is required to have a precisely rolling properties is affected due to inclusion of a foreign matter (dust) in a rust-preventive oil. In particular, in the case of a bearing for a precision machine and electronic machine and components, a large amount of an ultrapure solvent is required to wash such foreign matter off and remove it.
As explained above, when a preservation method using a rust-preventive oil is employed, it is necessary to remove the rust-preventive oil and dust contained in the rust-preventive oil. When oil and dust have a bad influence on not only a bearing but also other parts in a precision machine and a electronic machine and component in particular, it is indispensable to remove the oil and dust before use, and for this reason, a complicated working and the use of a large amount of a solvent are required. As a result, a product price increases and the solvent causes environmental contamination.
It is the sixth object of this invention to provide a method for preserving a bearing, which can be put to practical use even without using any rust-preventive oil.
A copper powder, silver powder, iron powder, rare earth metals, lead, tin and a powder of these (to be simply referred to as "a metal powder" hereinafter) are mainly used as a material for a sintered part of a machine and electronic machine and component, magnetic substance, solder, electrically conductive paste, etc. A carbon powder is sintered and used as a magnetic substance, heat-resistant part, etc. These powders are easily oxidized when exposed in air, which oxidation causes undesirable results such as a decrease in strength of a sintered part, a decrease in magnetic density, a decrease in solder adhesion and insulating properties, etc. Therefore, the oxidation of these powders is conventionally prevented by a method of substituting an inert gas such as nitrogen, argon, or the like for oxygen in a container (to be referred to as "gas substitution method" hereinafter), a method of enclosing them in a container together with a desiccant and sealing the container, a method of immersing them in an animal or plant oil, silicone oil, or the like, or some other methods.
However, in the gas substitution method, it is difficult to completely substitute an inert gas for oxygen and water among power particles, and the preservability is deteriorated due to oxygen and water which have permeated a packing material. A highly active powder undergoes oxidation even in the absence of water.
In a method of immersing them in an animal or plant oil or silicone oil, no desired strength is obtained when a powder is shaped under pressure and sintered. Hence, it is necessary to wash the animal or plant oil off with a solvent. The use of a large amount of the solvent deteriorates a working environment and affects natural environment. Organohalogen-containing solvents such as a Freon compound, e.g. trichlorofluoromethane, trihaloethane, trihalomethane, etc., used for the above washing cause environmental destruction, and it is therefore desired to decrease them.
Such a conventional method for preserving powders being oxidized has a limitation in preservation, and there are some highly active powders which cannot be preserved by this method. A manufacture for these powders being oxidized having a problem in preservation is required to manufacture such powders only after receipt of an order due to difficulty in preservation, and the manufacturer is required to have excess facilities and labor force. A user is also required to be punctual for a delivery term and strictly observe the time for use. These make steps, other documentation, etc., complicated uselessly and cause a useless increase in a cost.
It is the seventh object of this invention to develop a technique which can overcome the above defects of conventional methods and permit preservation of powders being oxidized simply and securely.
When a shadow mask formed of iron, a lead frame formed by plating a part or entire surface of an iron or iron-nickel alloy sheet with silver or gold, and the like are exposed to air, rust is formed on the surface thereof, and disadvantageously, problems such as contamination with dust, a decrease in solder-adhesion to a printing board, etc., arise. In particular, dew is formed due to a drastic change in temperature and humidity during the transportation abroad by air, and formation of rust is Promoted. The following methods have been proposed to prevent the rust formation.
(1) Method by gas substitution
Japanese Patent Publication Kokai No. 139370/1989 proposes a method in which nitrogen gas is substituted for air in a container. This method, however, has the following defects. A special apparatus is required for gas substitution, it is difficult to carry out efficient gas substitution in a container, it is difficult to achieve the object of this method even if a large amount of nitrogen gas is used, and the like.
(2) Method using nitrogen gas substitution and desiccant in combination
Japanese Patent Publication Kokai No. 139380/1989 proposes a method using nitrogen gas substitution and a desiccant in combination. However, this method also has the same defects as those in above (1).
And, the humidity inside the system increases due to water which has penetrated through a packing material, and the presence of the desiccant alone is not sufficient to prevent water on a metal surface from forming dew due to a drastic change in temperature and humidity during the transportation.
It is the eighth object of this invention to make it possible to transport metals and products including metals abroad without causing rust and with keeping them intact.